Is it safe if I redirect some of the propane heat so it warms up the blinker fluid to the proper operating temp?Best option is to hook up a propane heater and direct the airflow straight to the grill. Be careful not to get too close to the front though, less you melt the paint.
You'll want to wait on starting the engine until the average temp of the engine bay is between 60-80 degrees Fahrenheit.
Once started, wait exactly 10 minutes. Too little and the ECU won't be able to get enough readings to properly adjust to the real ambient air temperature without the propane heater. Too long and there will be too many readings (same issue).
Now, at the ten minute mark turn the engine off. Then Quickly turn off the heater and store safely. Don't take too long as the engine can cool faster than most think. Especially if the Temps are sub 20 degrees Fahrenheit. Take too long to do this and you'll have to restart the procedure all over again.
Once done, next Remote Start the Jeep. If you don't have remote start, then you'll have to start it with the driver door ajar. The goal is to let the Jeep know you don't intend to immediately drive off so it goes into a warm-up procedure.
Remember the ambient temperature of the engine bay before? Yup, the Jeep didn't go into a warm up procedure then because it detected warm air already. BUT NOW it'll detect the cold air...
Here's the bit that Jeep screwed up from factory. We've just forced the Jeep to warm up in a safe controlled manner. The Jeep now does its automated warm up procedure (#ECU Code WMU420) and makes sure proper fluid pressure and rpms are ran to safe operating parameters. IF WE DIDN'T warm the engine up ourselves, then the initial pressures would have been all over the map. This is ok a few times, but for us that live in crazy weather states like FL; having to warm the engine up in cold temperatures every day for months on end will result in blown head gaskets.
With the Jeep started, listen for the RPMs to run normal/settle towards idle as specified in your manual. At this point, she's safe to drive all you want!
Hope this helps!